<?php
$string1 = "TATAGTTTCCTCTCTATAT";
$string2 = "AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA
AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA
 AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA
 AAAGCCTCAAATCTCTCTAGTAAAAAAGCCTCAAATCTCTCTAGTAAA";

echo preg_replace('/[ \n\r]/', '', $string1 . $string2);
?>